U.S. patent application number 10/925047 was filed with the patent office on 2005-02-03 for near-field optical probe for reproducing information on a recording medium using near-field light.
This patent application is currently assigned to SEIKO INSTRUMENTS INC.. Invention is credited to Chiba, Norio, Kasama, Nobuyuki, Kato, Kenji, Mitsuoka, Yasuyuki, Niwa, Takashi, Oumi, Manabu.
Application Number | 20050025032 10/925047 |
Document ID | / |
Family ID | 12201392 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050025032 |
Kind Code |
A1 |
Oumi, Manabu ; et
al. |
February 3, 2005 |
Near-field optical probe for reproducing information on a recording
medium using near-field light
Abstract
A near-field optical probe has a planar substrate formed with a
through-hole and a phase shifter layer translucent to light having
a wavelength of illumination light used to illuminate the substrate
for producing near-field light. The phase shifter layer is
effective to cause a shift of phase in the illumination light by
180 degrees and is provided on the substrate so as to cover one
opening of the through-hole to form a microscopic aperture for
producing near-field light.
Inventors: |
Oumi, Manabu; (Chiba-shi,
JP) ; Mitsuoka, Yasuyuki; (Chiba-shi, JP) ;
Chiba, Norio; (Chiba-shi, JP) ; Kasama, Nobuyuki;
(Chiba-shi, JP) ; Kato, Kenji; (Chiba-shi, JP)
; Niwa, Takashi; (Chiba-shi, JP) |
Correspondence
Address: |
Bruce L. Adams
Adams & Wilks
31st Floor
50 Broadway
New York
NY
10004
US
|
Assignee: |
SEIKO INSTRUMENTS INC.
|
Family ID: |
12201392 |
Appl. No.: |
10/925047 |
Filed: |
August 24, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10925047 |
Aug 24, 2004 |
|
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10367138 |
Feb 14, 2003 |
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6831887 |
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Current U.S.
Class: |
369/118 ;
369/112.27; 369/13.33; G9B/7.097; G9B/7.165 |
Current CPC
Class: |
G11B 7/24 20130101; B82Y
10/00 20130101; G11B 7/005 20130101; G11B 7/12 20130101 |
Class at
Publication: |
369/118 ;
369/013.33; 369/112.27 |
International
Class: |
G11B 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 3, 1999 |
JP |
11-26728 |
Claims
1-5. (canceled).
6. A near-field optical probe comprising: a planar substrate formed
with a through-hole; and a phase shifter layer translucent to light
having a wavelength of illumination light used to illuminate the
substrate for producing near-field light, the phase shifter layer
being effective to cause a shift of phase in the illumination light
by 180 degrees and being provided on the substrate so as to cover
one opening of the through-hole to form a microscopic aperture for
producing near-field light.
7. A near-field optical probe according to claim 6; wherein the
phase shifter layer comprises a half-tone-type phase shifter
layer.
8. A near-field optical probe according to claim 6; wherein the
phase shifter layer has a transmittance of approximately 1/5 or
lower of an intensity of the produced near-field light.
9. In combination: a near-field optical probe according to claim 6;
and a near-field recording medium for storing information
reproducible utilizing near-field light produced by the near-field
optical probe.
10. A near-field optical probe, comprising: a planar substrate
formed with a through-hole; a shade film opaque to light having the
wavelength of illumination light used for illuminating the
substrate for producing near-field light, the shade film being
provided on the substrate so as to cover one opening of the
through-hole and having a first microscopic aperture for producing
near field light; and a phase shifter layer transparent to light
having the wavelength of the illumination light to cause a shift of
phase in the illumination light by 180 degrees, the phase shifter
layer being provided on the shade film to cover the first
microscopic aperture and having a second microscopic aperture
smaller than the first microscopic aperture.
11. In combination: a near-field optical probe according to claim
10; and a near-field recording medium for storing information
reproducible utilizing near-field light produced by the near-field
optical probe.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a recording medium reproducible by
utilizing near-field light and a near-field optical probe for
reproducing information recorded on such a recording medium and,
more particularly to-a recording medium and near-field optical
probe that enhances reproducing resolution for information recorded
with density.
[0002] In recent years, remarkable development has been made in
optical reproducing apparatuses (DVD players, etc.) for reproducing
information on recording media by illuminating laser light.
However, the information recording density has reached a limitation
because of a presence of a diffraction limit of laser light. In an
attempt to break through such diffraction limit, a proposal has
been made on a near-field light reproducing apparatus using an
optical head provided with a microscopic aperture having a diameter
of less than a wavelength of laser light to be utilized in
reproducing so that near-field light (including both near field and
far field) produced at the microscopic aperture or on a surface of
the recording medium can be utilized, thereby increasing
reproducible information recording density.
[0003] Conventionally, the near-field microscopes using a probe
(hereinafter referred to as a near-field optical probe) having a
microscopic aperture as mentioned above as an apparatus utilizing
near-field light have been utilized for observing sample
microscopic surface textures. As one of schemes utilizing
near-field light in the near-field microscopes, there is a scheme
that the near-field optical probe microscopic aperture and the
sample surface are approached in distance to nearly a diameter of
the near-field optical probe microscopic aperture so that
near-field light can be produced at the microscopic aperture by
introducing propagation light through the near-field optical probe
and toward the near-field optical probe microscopic aperture
(illumination mode). In this case, scattering light caused by the
interaction between the produced near-field light and the sample
surface involving an intensity and phase reflecting a sample
surface microscopic texture is detected by a scattering light
detection system. Thus, high resolution of observation is made
feasible that could not be achieved by the conventional optical
microscopes.
[0004] There is another scheme of the near-field microscopes
utilizing near-field light that propagation light is illuminated
toward a sample to localize near-field light over the sample
surface wherein a near-field optical probe microscopic aperture is
approached to the sample surface to nearly a diameter of the
near-field optical probe microscopic aperture (collection mode). In
this case, scattering light cause by the interaction between the
localized near-field light and the near-field optical probe
microscopic aperture involving an intensity and phase reflecting a
sample surface microscopic texture is guided to a scattering light
detection system through the near-field optical probe microscopic
aperture, thus achieving observation with high resolution.
[0005] As a near-field microscope, Japanese Patent Laid-open No.
174542/1995, for example, has been proposed disclosing a scanning
near-field atomic force microscope. This scanning near-field atomic
force microscope adopts as near-field optical probe an optical
waveguide sharpened at a tip to perform probe access control and
scanning control for the atomic force microscope (AFM) thereby
enabling observation of sample surface topology and optical
characteristics. FIG. 11 is a block diagram showing a schematic
configuration of the scanning near-field atomic force
microscope.
[0006] In FIG. 11, a scanning near-field atomic force microscope 80
has, above a probe 89, a laser light source 83, a focus lens 84, a
mirror 85 and a photoelectric conversion element 86 vertically
divided into two. The light emitted from the laser light source 83
is collected by the focus lens 84 onto a probe top surface 82 so
that the light reflected thereon is guided to the photoelectric
conversion element 86 via the mirror 85. Meanwhile, the light
emitted from a light source 94 for light information measurement is
illuminated through a collimate lens 95 to a backside of a
recording medium 81 over a prism 92 having a slant face treated for
total reflection. Then, the light is guided to the other end of the
probe 89 (not-sharpened base) that is proximate to the recording
medium 81 and introduced to the photoelectric conversion element
87.
[0007] The prism 92 and recording medium 81 are set up on a rough
movement mechanism 97 and fine movement mechanism 96 movable in XYZ
directions. The signal detected by the photoelectric conversion
element 86 is sent to a servo mechanism 93. Based on the signal,
the servo mechanism 93 controls the rough movement mechanism 97 and
fine movement mechanism 96 so that the deflection on the probe 89
cannot exceed a prescribed value when approaching of the probe 89
to the recording medium 81 or reading out data. The servo mechanism
93 is connected with a computer 99 to control operation of the fine
movement mechanism 96 in a planar directions and receive
information about the recording medium from a control signal of the
servo mechanism 93. Meanwhile, when applying modulation to the
light of the light source 94 or providing vibration by a vibration
mechanism 88 to between the probe 89 and the recording medium 81,
the signal obtained in the photoelectric conversion element 87 is
connected to an analog input interface of the computer 99 via a
lock-in amplifier 98 to detect optical information in synchronism
with planar action of the fine movement mechanism 96. When no
modulation or the like is applied to the light source 94, the
signal obtained in the photoelectric conversion element 87 is
directly connected to the analog input interface of the computer 99
without being passed through the lock-in amplifier 98.
[0008] The above near-field optical information reproducing
apparatus utilizes the near-field microscope technology and
observation scheme, and can reproduce information densely recorded
on a recording medium by utilizing near-field light.
[0009] However, where the recording medium is increased in
recording density by arranging data marks as information units in a
close relationship, when conducting reproducing with the recording
medium there encounters difficulty for the near-field optical probe
used in the conventional near-field optical information reproducing
apparatus to individually recognize and detect adjacent ones of the
data marks. This problem is explained hereinbelow on an example of
a near-field optical probe of a near-field optical information
reproducing apparatus for information reproducing on the collection
mode. FIG. 12 shows a recording medium 100 arranged with data marks
101 to produce near-field light. Incidentally, FIG. 12 shows one
part of the recording medium 100 wherein the dotted circle 102
signifies a position that a data mark is possible to provide.
[0010] In FIG. 12 the data marks 101 are different in optical
transmittance or refractive index, for example, from a base member
103 of the recording medium 100. The difference in optical property
enables recognition of the presence or absence of a data mark 101.
That is, in the data mark 101 the near-field light produced on a
surface of the recording medium 100 is different in intensity or
the like from that of the base material 103, which realizes to
reproduce information configured by the data mark 101. Here, the
near-field light on the surface of the recording medium 100 is
produced by illuminating incident light, such as laser light, at a
backside (surface not having data marks) of the recording medium
100 under a condition of total reflection. Incidentally, recording
onto the data mark 101 is possible to realize by a phase change
recording method or the like in the currently-marketed rewritable
recording mediums.
[0011] FIG. 13 shows a relationship between a sectional view of the
recording medium 100 taken on line D-D' in FIG. 12 and near-field
light produced by the data marks 101. Meanwhile, in FIG. 13, a
near-field optical probe 110 is arranged above the recording medium
100. The near-field optical probe 110 moves in a rightward
direction in the figure as scanning directions to sequentially
detect near-field light produced through the data marks 101 of the
recording medium 100. For example, provided that in FIG. 13 the
regions recorded with a data mark 101 (101a, 101b, 101c) are taken
as "1" while those not recorded with a data mark 101 is as "0", a
signal will be reproduced as "01101" from left of the figure.
[0012] Accordingly, the amplitude of near-field light in positions
fully close to the corresponding data marks 101a, 101b, 101c to "1"
can be expressed rectangular, in an ideal case, as represented in a
near-field light amplitude distribution of FIG. 13 (on medium
surface). With respect to this, a near-field light amplitude
distribution (at microscopic opening) of FIG. 13 shows a near-field
light amplitude distribution of near-field light reaching a
microscopic aperture 111 of the near-field optical probe 110, i.e.
at a position that a given distance is provided between the data
mark 101 and the near-field optical probe 110. Each data mark 101
has a spread smoothly attenuating left and right with a maximum
point given on a center axis of the data mark.
[0013] Meanwhile, a near-field light intensity distribution (at
microscopic aperture) of FIG. 13 illustrates a near-field light
intensity distribution offered by the above near-field light
amplitude distribution (at microscopic aperture). As is shown,
near-field light produced through the adjacent data marks 101a and
101b at a position reaching the microscopic aperture 111 of the
near-field optical probe 110 overlaps at respective foots of
near-field light amplitude. This results in an obscured boundary
between near-field light produced through the data mark 101a and
near-field light produced through the data mark 101b, thus lowering
resolution in reproducing. Thus, the data marks are difficult to
separately recognize in the microscopic aperture 111 position of
the near-field optical probe 110.
[0014] The near-field optical information reproducing apparatus is
to ultimately detect a data mark 101 or reproduce information by
guiding, into a near-field optical probe, scattering light
(propagation light) obtained by scattering near-field light
reaching the microscopic aperture 111 of the near-field optical
probe 110. Consequently, the problem with data mark separation is
not negligible. This problem might be avoided by providing full
spacing between the data marks 101. This however decreases
recording density on the recording medium, impairing high-density
recording medium reproducing as a merit of near-field optical
information reproducing apparatus.
[0015] Meanwhile, in illumination-mode information reproducing, in
order to separately recognize individual data marks densely
arranged on a recording medium, it is possible to decrease a
localization range of near-field light caused at the microscopic
aperture by reducing the size of the microscopic aperture of the
near-field optical probe. However, a high level technology is
required to make smaller microscopic aperture. There encounters a
problem that a decreased localized range of near-field light is
also decreased in intensity and hence difficult to detect.
SUMMARY OF THE INVENTION
[0016] It is an object of the present invention to provide a
recording medium and near-field optical probe which can achieve
high density information recording and enhance resolution in
reproducing.
[0017] In order to achieve the above object, a first recording
medium according to the present invention is a recording medium
formed on a recording medium surface with information reproducible
by utilizing near field light, comprising: a medium base member
transparent for a wavelength of illumination light (incident light)
to be illuminated to produce the near field light; a phase shifter
arrangement layer arranged alternately, in a direction parallel
with a surface of the medium base member and in a reproducing
direction of the information, with transmission regions transparent
for the wavelength of the illumination light and phase shifter
regions transparent for the wavelength of the illumination light to
cause a shift of phase in the illumination light by 180 degrees;
and a data mark arrangement layer formed on the phase shifter
arrangement layer and having data marks as units of the information
respectively corresponding one by one to the transmission regions
and the phase shifter regions.
[0018] According to this invention, on a base member (medium base
member) having a sufficient transmittance for a wavelength of
incident light to be illuminated at the backside of the recording
medium where a near field light information reproducing apparatus
adopts a collection mode as a reproducing scheme, a phase shift
arrangement layer is provided which is formed alternately with a
phase shifter region transparent for the wavelength of the incident
light to be illuminated at the backside of the recording medium
under a condition of total reflection to cause a 180-degree shift
of phase in the incident light and a transmission region
transparent for the wavelength of the incident light. Furthermore,
a data mark arrangement layer is formed that a row of data marks
can be arranged in positions on the phase shifter regions and
transmission regions. It is therefore possible to cause
cancellation between spread of near field light caused on the
recording medium due to incident light transmitted through the
phase shifter regions and spread of near field light caused on the
recording medium due to incident light transmitted through the
transmission regions.
[0019] Also, in a second recording medium of the invention, in the
first recording medium the data mark arrangement layer has a shade
film formed on a surface thereof in regions except for those having
the data marks, to shade from the illumination light.
[0020] According to the invention, the shade film is coated on the
surface of the data mark arrangement layer in areas except for the
data marks and those where data marks are possible to provide.
Accordingly, near-field light only is obtained on the surface of
the recording medium for illumination light incidence under other
conditions than total reflection.
[0021] Also, a third recording medium according to the present
invention is a recording medium formed on a recording medium
surface with information reproducible by utilizing near field
light, comprising: a medium base member transparent for a
wavelength of illumination light to be illuminated to produce the
near field light; a phase shifter translucent for the wavelength of
the illumination light to cause a shift of phase in the
illumination light by 180 degrees; wherein the phase shifter is
provided on a surface of the medium base member in areas except
those for producing the near field light and having data marks as
units of the information.
[0022] According to this invention, on a base member (medium base
member) having a sufficient transmittance for a wavelength of
illumination light (laser light or the like) to be illuminated at
the backside of the recording medium where a near field light
information reproducing apparatus adopts a collection mode as a
reproducing scheme, a phase shifter is coated, which is translucent
for the wavelength of illumination light to be illuminated at the
backside of the recording medium to cause a 180-degree shift of
phase in the laser light wherein an opening not coated with the
phase shifter is arranged as a data mark as information unit. It is
therefore possible to cancel between spread at data mark edges of
near field light caused through the data mark and spread at phase
shifter edges of near field light.
[0023] Also, a first near field optical probe according to the
present invention is a near field optical probe having a
microscopic aperture for producing near field light, comprising: a
planar substrate formed with a through-hole; and a phase shifter
translucent for a wavelength of illumination light to be
illuminated for producing the near field light to cause a shift of
phase in the illumination light by 180 degrees; wherein the phase
shifter is provided in a manner closing one opening of the
through-hole to have the microscopic aperture.
[0024] According to this invention, the phase shifter is formed at
the opening of the through-hole of the near field optical probe
which is translucent for a wavelength of laser light (illumination
light) to be introduced to the through-hole to cause a 180-degree
shift of phase in the laser light. Furthermore, the microscopic
aperture is formed in the phase shifter to have an appropriate
diameter for producing near field light. Accordingly, in the case
that the reproducing scheme to be adopted in a near field light
information reproducing apparatus is taken an illumination mode,
cancellation is made between spread in near field light produced
through the microscopic aperture and spread in propagation light
transmitted through the phase shifter, at their respective
edges.
[0025] Also, a second near field optical probe according to the
present invention is a near field optical probe having a
microscopic aperture for producing near field light, comprising: a
planar substrate formed with a through-hole; a shade film opaque
for a wavelength of illumination light to be illuminated for
producing the near field light; and a phase shifter transparent for
the wavelength of the illumination light to be illuminated for
producing the near field light to cause a shift of phase in the
illumination light by 180 degrees; wherein the shade film is
provided in a manner closing one opening of the through-hole to
have a first microscopic aperture for producing the near field
light; and the phase shifter being provided in a manner closing the
first microscopic aperture to have a second microscopic aperture
smaller than said first microscopic aperture.
[0026] According to this invention, the first microscopic aperture
for producing near field light is formed by locally coating the
shade film. The phase shifter is formed in a manner closing the
first microscopic aperture, which is transparent for a wavelength
of laser light (illumination light) to be introduced to the
through-hole to cause a 180-degree shift of phase in the laser
light. The second microscopic aperture is provided in the phase
shifter. Accordingly, in the case that the reproducing scheme to be
adopted in a near field light information reproducing apparatus is
taken an illumination mode, cancellation is made between spread in
near field light produced through the first microscopic aperture
and spread in second near field light transmitted through the phase
shifter, at their respective edges. Thus, it is possible to obtain
near field light with sharpness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is an illustrative view showing one part of a
recording medium according to Embodiment 1;
[0028] FIG. 2 is an illustrative representation showing a
relationship between a sectional view of the recording medium taken
on line A-A' in FIG. 1 and near-field light produced through data
marks thereof;
[0029] FIG. 3 is an illustrative view showing one part of a
recording medium according to Embodiment 2;
[0030] FIG. 4 is an illustrative representation showing a
relationship between a sectional view of the recording medium taken
on line B-B' in FIG. 3 and near-field light produced through data
marks thereof;
[0031] FIG. 5 is an illustrative view showing one part of a
recording medium according to Embodiment 3;
[0032] FIG. 6 is an illustrative representation showing a
relationship between a sectional view of the recording medium taken
on line C-C' in FIG. 5 and near-field light produced through data
marks thereof;
[0033] FIG. 7 is a schematic structural view showing a near-field
optical probe according to Embodiment 4;
[0034] FIG. 8 is an illustrative representation showing a
relationship, in the near-field optical probe of Embodiment 4,
between a phase shifter portion, propagation light transmitted
through a vicinity of a microscopic aperture and near-field light
produced through the microscopic aperture;
[0035] FIG. 9 is a schematic structural view showing a near-field
optical probe according to Embodiment 5;
[0036] FIG. 10 is an illustrative representation showing a
relationship, in the near-field optical probe of Embodiment 5,
between first near-field light and second near-field light;
[0037] FIG. 11 is a block diagram showing a schematic structure of
a conventional scanning near-field atomic force microscope;
[0038] FIG. 12 is an illustrative view showing a conventional
recording medium utilizing near-field light; and
[0039] FIG. 13 is an illustrative representation showing a
relationship between a sectional view of the recording medium taken
on line D-D' in FIG. 12 and near-field light produced through data
marks thereof;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] Embodiments of the present invention will now be described
with reference to the accompanying drawings, which is on recording
medium to be reproduced utilizing near-field light and information
reproducing apparatus therefor. Note that the invention is not
limited by the embodiments.
Embodiment 1
[0041] Referring to FIG. 1, there is illustrated one part of a
recording medium according to Embodiment 1 of the present
invention. A recording medium 10 in the figure includes a substrate
having a sufficient transmittance of light to produce near-field
light, on which is formed a phase shifter arrangement layer,
hereinafter referred to. Furthermore, a data mark arrangement layer
is formed on the phase shifter arrangement layer. Herein, the data
mark arrangement layer is a region to be formed with a data
mark.
[0042] In FIG. 1, the recording medium 10 has a data mark
arrangement layer to be formed with data marks 11 serving as the
light transmittance regions to produce comparatively intense
near-field light, for example. The proper arrangement of data marks
11 makes possible to achieve information recording. Note that in
the figure the circle 12 depicted by a dotted line represents a
position that a data mark is possible to provide therein. It is
assumed herein that the data mark 11 corresponds to information of
a logical value "1" while the dotted circle 12, or area having no
data mark 11, to a logical value "0".
[0043] In this embodiment, the data mark 11 is provided by a
material or physical structure that near-field light to be produced
can be intensified by a difference in refractive index or optical
absorbance from that of the area (dotted circle 12) having no data
mark 11. Alternatively, it may be of other materials or physical
structures that is to be distinguished based upon a difference in
optical property, such as polarizing light direction and absorption
coefficient.
[0044] As shown in FIG. 1, a shade film 13 is coated over a surface
in areas except for those to have data marks 11, in order to
prevent incident light from appearing at a surface that is
illuminated at a backside of the recording medium 10. This shade
film 13 eliminates the necessity of precisely controlling a
direction of incident light illuminated to the recording medium 10
at the backside, without providing especial total reflection
conditions.
[0045] The phase shifter arrangement layer positioned underlying
the data mark arrangement layer, as illustrated, is in an
arrangement alternate with a phase shifter region 14 and a
transmission region 15 having no phase shifter. The transmission
region 15 is preferably formed of a same material as the recording
medium 10, i.e. a transparent material transmissible of incident
light. The data marks 11 are arrayed in lengthwise rows of the
phase shifter region 14 and transmission regions 15, depending upon
information to be recorded. It however is noted that the data marks
11 are to be detected of presence or absence with respect to a
vertical direction to a lengthwise direction of the phase shifter
regions 14 and transmission regions 15.
[0046] Here, the phase shifter region is formed of a transparent
material having a sufficiently great transmittance for a wavelength
of incident light illuminated at a backside of a recording medium
10 to have a phase difference of 180 degrees with respect to a base
member of the recording medium 10, e.g. applied glass film or
sputtered SiO.sub.2 film.
[0047] Referring to FIG. 2, there is illustrated a figure showing a
relationship between a sectional view of the recording medium 10
taken on line A-A' in FIG. 1 and near-field light produced by the
data marks 11. In the figure, the recording medium 10 is structured
by a base member 16 formed of a sufficiently transmissible material
of incident light under conditions other than total reflection, a
phase shifter arrangement layer formed on the base member, and a
data mark arrangement layer formed thereon.
[0048] Also, in FIG. 2 a near-field optical probe 8 is arranged
above the recording medium 10. The near-field optical probe 8 moves
in a rightward direction of the figure as a scanning direction, to
thereby detect near-field light produced at the data marks 11
arranged on the recording medium 10 in a sequential fashion.
Assuming for example that data mark 11 recorded regions (11a, 11b,
11c) are given "1" and data mark 11 non-recorded regions "0", a
signal will be produced as "01101" with respect to a left-to-right
direction of the figure in regions shown in FIG. 2.
[0049] Accordingly, near-field light positioned fully close to the
data marks 11a, 11b, 11c each corresponding to "1" has an amplitude
that can be expressed as a rectangular wave, as ideally shown in
near-field light amplitude distribution (on medium surface) of FIG.
2. Here, in the near-field light amplitude distribution (on medium
surface), in a minus region is exhibited a near-field light
produced due to transmission through the phase shifter region 14.
That is, near-field light produced over the phase shifter region 14
is inverted in phase by 180 degrees with respect to near-field
light produced due to transmission through the transmission region
15.
[0050] With respect to this, a near-field light amplitude
distribution (at microscopic aperture) of FIG. 2 shows an amplitude
distribution of near-field light reaching a microscopic aperture 9
of the near-field optical probe 8, i.e. near-field light in a
position that a given distance is provided between the data mark 11
and the near-field probe 8. In this near-field light amplitude
distribution (at microscopic opening), illustrated is a
distribution having spreads smoothly attenuated left and right with
maximum points given on data-mark center axes, i.e. in the plus
region concerning the data mark 11a and in the minus region
concerning the data marks 11b and 11c.
[0051] Meanwhile, a near-field light intensity distribution (at
microscopic aperture) of FIG. 2 shows a near-field light intensity
distribution offered by the above-stated near-field light amplitude
distribution (at microscopic aperture). That is, shown is an
absolute value of a sum of a near-field light amplitude caused on
the surface of the recording medium 10 due to incident light passed
through the transmission regions 15 and a near-field light
amplitude caused on the surface of the recording medium 10 due to
incident light passed through the phase shifter regions 14. As is
shown, near-field light produced through the adjacent data marks
11a and 11b is made clear at boundaries by the presence of a near
field light in the minus region due to the phase shifter regions 14
although it has conventionally been unclear at near-field light
boundaries due to overlapped foots in near-field light amplitude
between adjacent data marks. That is, it becomes possible to
separately recognize adjacent data marks.
[0052] As described above, according to the recording medium 10 of
Embodiment 1, on a base member 16 having a sufficient transmittance
for a wavelength of incident light illuminated at the backside of
the recording medium 10 where a near-field light information
reproducing apparatus adopts a collection mode as a reproducing
scheme, a phase shift arrangement layer is provided which is formed
alternately with a phase shifter region 14 transparent for the
wavelength of the incident light illuminated at the backside of the
recording medium 10 to cause 180-degrees shifting in phase of
incident light and a transmission region 15 transparent for the
wavelength of the incident light. Furthermore, a data mark
arrangement layer is formed which can be arranged with a row of
data marks 11 in respective positions over the phase shifter
regions 14 and the transmission regions 15. A shade film 13 is
formed over an area except for areas with data marks 11 and areas
that data marks are possible to provide. Accordingly, cancellation
is made between spread of near-field light caused on the recording
medium 10 due to incident light transmitted through the phase
shifter regions 14 and spread of near-field light caused on the
recording medium 10 due to incident light transmitted through the
transmission regions 14. This makes it possible to improve the
contrast of near-field light in the areas of the adjacent data
marks 11 or those that the data marks 11 are adjacently provided.
Due to this, it is possible to reduce the distance between the
adjacent data marks 11 and hence improve recording density.
Embodiment 2
[0053] Explanations will be now made on a recording medium
according to Embodiment 2. FIG. 3 shows one part of the recording
medium of Embodiment 2. The recording medium 20 of FIG. 3 is
different from the recording medium 10 according to Embodiment 1
only in that no shade film is coated over a surface of the
recording medium. Accordingly, the recording medium 20 of FIG. 3 is
structured by a phase shifter arrangement layer formed on a base
member having a sufficient transmittance for producing near-field
light, and a data mark arrangement layer formed on the phase
shifter arrangement layer.
[0054] Here, the phase shifter arrangement layer is formed
alternately with a phase shifter regions 24 and transmission
regions 25 similarly to Embodiment 1 while the data mark
arrangement layer is a region where data marks 21 are to be formed.
Note that circles 22 shown by dotted lines in the figure represent
positions that data marks are possible to provide.
[0055] Meanwhile, in FIG. 1 the shade film is not formed on the
surface in areas except for areas that data marks 21 are possible
to provide. Accordingly, in the case that incident light is
illuminated at an arbitrary angle with respect to the backside of
the recording medium 20 (including a vertical direction) as in
Embodiment 1, there is encountered inconvenience that the incident
light will appear at the surface. Consequently, there is a
necessity of illuminating such incident light to the backside of
the recording medium 20 at an angle of total reflection, thereby
causing near-field light only due to oozing in the surface of the
recording medium 20.
[0056] Referring to FIG. 4, there is illustrated a relationship
between a sectional view of the recording medium 20 taken on line
B-B' in FIG. 3 and near-field light caused through the data marks
21. In the figure, the recording medium 20 is structured by a phase
shifter arrangement layer as stated above and a data mark
arrangement layer provided thereon, on a base member 26 formed of a
sufficiently transmissible material for an oozing portion of the
incident light illuminated under a condition of total
reflection.
[0057] In FIG. 4 a near-field optical probe 8 is also arranged
above the recording medium 20, similarly to FIG. 2. The near-field
optical probe 8 moves in a rightward direction of the figure as a
scanning direction to thereby detect near-field light produced at
the data marks 21 arranged on the recording medium 20 in a
sequential fashion.
[0058] Accordingly, near-field light positioned fully close to the
corresponding data marks 21a, 21b, 21c to "1" has an amplitude that
can be expressed as a rectangular wave, as ideally shown in
near-field light amplitude distribution (on medium surface) of FIG.
4, similarly to FIG. 2. However, the difference from FIG. 2 lies in
that there are no regions where the amplitude of near-field light
becomes 0 because no shade film exists between the data marks.
[0059] With respect to this, the near-field light amplitude
distribution (at microscopic aperture) of FIG. 4 shows an amplitude
distribution of near-field light reaching the microscopic aperture
9 of the near-field optical probe 8. In this near-field light
amplitude distribution (at microscopic opening), there is
illustrated a distribution having spreads smoothly attenuated left
and right with maximum points on data-mark center axes, i.e. in the
plus region for the data mark 21a and in the minus region for the
data marks 11b and 11c. Particularly, near-field light at portions
where no data mark is positioned is in a form of broad
spreading.
[0060] Meanwhile, a near-field light intensity distribution (at
microscopic aperture) of FIG. 4 illustrates a near-field light
intensity distribution offered by the above-stated near-field light
amplitude distribution (at microscopic aperture). That is, there is
shown an absolute value of a sum of a near-field light amplitude
caused on the surface of the recording medium 20 due to incident
light passed through the transmission regions 25 and a near-field
light amplitude caused on the surface of the recording medium 20
due to incident light passed through the phase shifter regions 24.
As is shown, near-field light produced through the data marks 21a
and 21b is made clear at boundaries. That is, it becomes possible
to separately recognize the adjacent data marks.
[0061] As described above, according to the recording medium 20 of
Embodiment 2, on a base member 26 having a sufficient transmittance
for a wavelength of incident light illuminated at the backside of
the recording medium 20 where a near-field light information
reproducing apparatus adopts a collection mode as a reproducing
scheme, a phase shifter arrangement layer is provided which is
formed alternately with a phase shifter region 24 transparent for
the wavelength of the incident light illuminated at the backside of
the recording medium 20 under a condition of total reflection to
cause 180-degrees shifting in phase of the incident light and a
transmission region 25 transparent for the wavelength of the
incident light. Furthermore, a data mark arrangement layer is
formed which can be arranged with a row of data marks 21 in
respective positions over the phase shifter regions 24 and the
transmission regions 25. Accordingly, cancellation is made between
spread of near-field light caused on the recording medium 20 due to
incident light transmitted through the phase shifter regions 24 and
spread of near-field light caused on the recording medium 20 due to
incident light transmitted through the transmission regions 25.
This makes it possible to improve the contrast of near-field light
in areas of adjacent data marks 21 or those that the data marks 21
are adjacently provided. Due to this, it is possible to reduce the
distance between the adjacent data marks 21 and hence improve
recording density.
[0062] Further, there is no necessity of forming the shade film
between the data marks 21. Accordingly it is possible to reduce
manufacturing processes for the recording medium and to form
adjacent data marks 21 in a closer relationship as compared to the
recording medium according to Embodiment 1.
Embodiment 3
[0063] Explanations will now be made on a recording medium
according to Embodiment 2. FIG. 5 shows one part of the recording
medium of Embodiment 3. The recording medium 30 of FIG. 5 has a
phase shifter 33 coated on a base member having a sufficient
transmittance for producing near-field light, and data marks 31
provided in areas not coated with the phase shifter 33 thus storing
information. Note that circles 32 shown by dotted lines represent
positions that data marks are possible to provide. Here, the phase
shifter 33 has a transmittance of approximately 2-20% for a
wavelength of an oozing portion of the incident light illuminated
at the backside of the recording medium 30 under a condition of
total reflection. The phase shifter is also formed of a translucent
material having a phase difference of 180 degrees with respect to
the base member 36 of the recording medium 30 (particularly, the
translucent phase shifter is referred to as a half-tone type phase
shifter), e.g. an applied glass film or sputtered SiO.sub.2
film.
[0064] Referring to FIG. 6, there is illustrated a relationship
between a sectional view of the recording medium 30 taken on line
C-C' in FIG. 5 and near-field light caused through the data marks
31. In the figure, a near-field optical probe 8 is also arranged
above the recording medium 30, similarly to FIG. 2. The near-field
optical probe 8 moves in a rightward direction of the figure as a
scanning direction, thereby sequentially detecting near-field light
produced by the data mark 31 on the recording medium 30.
[0065] Accordingly, near-field light positioned fully close to the
data marks 31a, 31b, 31c has an amplitude that can be expressed as
a rectangular wave, as ideally shown in near-field light amplitude
distribution (on medium surface) of FIG. 6, similarly to FIG. 2. In
this near-field light amplitude distribution (on recording medium),
in a minus region represents near-field light produced over the
phase shifter 33. That is, near-field light produced over the phase
shifter 33 has a phase difference of 180 degrees with respect to
near-field light produced over the data marks, and a sufficiently
low intensity due to a difference in transmittance as compared to
an intensity of near-field light produced over the data marks.
[0066] With respect to this, a near-field light amplitude
distribution (at microscopic aperture) of FIG. 6 shows an amplitude
distribution of a near-field light reaching the microscopic
aperture 9 of the near-field optical probe 8. That is, illustrated
is an amplitude distribution of near-field light in a position that
a given distance is provided between the data mark 31 and the
near-field optical probe 8. On the data marks are exhibited spreads
smoothly attenuated left and right with maximum points on data-mark
center axes in the plus region. In areas that the phase shifter 7
is coated, spreads are exhibited smoothly approaching 0 at edges of
data marks or phase shifter 33 in the minus region.
[0067] Meanwhile, a near-field light intensity distribution (at
microscopic aperture) of FIG. 6 exhibits a near-field light
intensity distribution offered by the above-stated near-field light
amplitude distribution (at microscopic aperture). That is, there is
shown an absolute value of a sum of a near-field light amplitude
caused through the data marks 31 and near-field light caused
through the phase shifter 33. In the conventional, near-field light
created through adjacent data marks 31a and 31b has been obscured
at its boundaries because of overlap in foot of near-field light
amplitude at the adjacent data marks as is shown. In the
embodiment, however, clarity is provided at the boundaries due to a
presence of near-field light in the minus region caused through the
phase shifter 33. It therefore becomes possible to separately
recognize data marks.
[0068] As described above, according to the recording medium 30 of
Embodiment 3, on a base member 36 having a sufficient transmittance
for a wavelength of laser light illuminated at the backside of the
recording medium 30 where a near-field light information
reproducing apparatus adopts a collection mode as a reproducing
scheme, a phase shifter 33 is provided which is translucent for a
wavelength of incident light illuminated at the backside of the
recording medium 30 under a condition of total reflection to cause
shifting in phase of the incident light by 180 degrees. Data marks
31 are provided in apertures not coated by the phase shifter 33.
Accordingly, cancellation is made between spread of near-field
light at edges of the data marks 31 and spreads of near-field light
at edges of the phase shifter 33. This makes it possible to improve
the contrast of near-field light through the data marks 31. Due to
this, it is possible to reduce the distance between the
adjacent-data marks 31 and hence improve recording density.
Embodiment 4
[0069] Explanations will now be made on a near-field optical probe
according to Embodiment 4. FIG. 7 illustrates a schematic
structural view of a near-field optical probe according to
Embodiment 4 of the invention. This near-field optical probe is
effective particularly for a case of an illumination mode mentioned
before. In the figure, a near-field optical probe 50 has a
through-hole 52 formed through a planar substrate 51, e.g. of a
silicon substrate, through utilizing a semiconductor manufacture
process. Meanwhile, a phase shifter 53 is formed over one opening
of the through-hole 32 in a manner closing the same. The phase
shifter 53 is formed through with a microscopic aperture 54. The
microscopic aperture 54 has an appropriate size for producing
near-field light, i.e. a diameter of several tens of
nanometers.
[0070] Here, the phase shifter 53 is a half-tone type phase shifter
similar to the phase shifter 33 explained in Embodiment 3. The
phase shifter causes incident light, such as laser light,
introduced at the opposite opening of the through-hole 52 to be
inverted (shifted by 180-degrees) in phase and transmitted through
with sufficient attenuation in light intensity. In particular, the
phase shifter 53 is required to have a transmittance of nearly
one-fifth or lower of the near-field light intensity to be produced
at the microscopic aperture 54, which is almost opaque rather than
translucent. The transmission light (including near-field light due
to oozing effect) is illuminated, together with near-field light
produced at the microscopic aperture 54, onto a surface of the
recording medium 40.
[0071] When near-field light 55 produced at the microscopic
aperture 54 is given onto the data mark 41 of the recording medium
40, it undergoes intense scattering due to the data mark 41 thus
producing scattering light. (propagation light). The scattering
light is detected by a not-shown photodetector and converted into a
reproduced signal, thus achieving recognition of the data mark
41.
[0072] Referring FIG. 8, there is illustrated a relationship
between a part of the phase shifter 53 of the near-field optical
probe 50 and propagation light transmitted through a vicinity of
the microscopic aperture 54 as well as near-field light produced
through the microscopic aperture 54. The amplitude of near-field
light in a position fully close to the microscopic aperture 54 can
be expressed rectangular as ideally shown in a near-field light
amplitude distribution (at microscopic aperture) of FIG. 8. In the
near-field light amplitude distribution (at microscopic aperture),
in a minus region is shown propagation light transmitted through
the phase shifter 53. That is, propagation light transmitted
through the phase shifter 53 is inverted in phase by 180 degrees
with respect to near-field light produced through the microscopic
aperture 54, and has sufficiently low intensity as compared to an
intensity of near-field light produced through the microscopic
aperture 54.
[0073] With respect to this, a near-field light amplitude
distribution (on medium surface) of FIG. 8 illustrates an amplitude
distribution of near-field light reaching the recording medium 40,
that is, an amplitude distribution of near-field light and
propagation light in a position that a given distance is provided
between the near-field optical probe 50 and the surface of the
recording medium 40. As concerned with near-field light 55 is
exhibited a spread smoothly attenuating left and right with a
maximum point given on a center axis of the microscopic aperture 54
in a plus region. For propagation light is exhibited a spread
smoothly approaching 0 at edges of the microscopic aperture 54 or
phase shifter 53 in a minus region.
[0074] Meanwhile, a near-field light intensity distribution (on
medium surface) of FIG. 8 shows a distribution in intensity of
near-field light and propagation light offered due to the above
near-field light amplitude distribution (on medium surface). That
is, shown is an absolute value of a sum of near-field light
amplitude produced through the microscopic aperture 54 and
propagation light produced through the phase shifter 53. As is
shown, near-field light produced through the microscopic aperture
54 is cut in spread of near-field light at the edges of the
microscopic aperture 54 due to a presence of propagation light
through the phase shifter 53 in the minus region, thus providing
near-field light distributed with greater sharpness.
[0075] As explained above, according to the near-field optical
probe 50 of Embodiment 4, the phase shifter 53 is formed at the
opening of the through-hole 52 of the near-field optical probe 50
which is translucent for a wavelength of incident light introduced
to the through-hole 52 to cause shifting by 180 degrees in the
phase of laser light. Furthermore, the microscopic aperture 54 is
formed in the phase shifter 53 to have an appropriate diameter for
producing near-field light. Accordingly, in the case that the
reproducing scheme to be adopted in a near-field light information
reproducing apparatus is taken an illumination mode, cancellation
is made between spread in near field light produced through the
microscopic aperture 54 and spread in propagation light transmitted
through the phase shifter 53, at their respective edges. Thus, it
is possible to obtain near-field light with sharpness. This can
provide interaction more locally to the data mark 21 arranged on
the recording medium 40. It is therefore possible to reproduce
information from the recording medium 40 having the data marks 41
recorded with density.
Embodiment 5
[0076] Explanation will be now made on a near-field optical probe
according to Embodiment 5. FIG. 9 illustrates a schematic
structural view of a near-field optical probe according to
Embodiment 5 of the invention. This near-field optical probe is
effective particularly for a case of an illumination mode,
similarly to Embodiment 4. In the figure, a near-field optical
probe 60 has a through-hole 62 formed through a planar substrate
61, e.g. of a silicon substrate, through utilizing a semiconductor
manufacture process. Meanwhile, the through-hole 62 at its one
opening has a shade film 65 to thereby form an aperture.
Furthermore, a phase shifter 63 is formed in a manner closing the
opening and covering the shade film 65. Sequentially, a microscopic
aperture 64 is formed through areas of the phase shifter 63 not
provided with the shade film 65 at its under layer e.g. by FIB
(Focused Ion Beam). Incidentally, the microscopic aperture 64 is
required smaller than the opening of the shade film 65. The shade
film 65 aperture and the microscopic aperture 64 are each in an
appropriate size for producing near field light, e.g. having a
diameter of several tens of nanometers.
[0077] Here, the phase shifter 63 is a transparent type shifter to
cause inversion (shift by 180 degrees) in the phase of incident
light introduced at the other opening of the through-hole 62,
allowing incident light to sufficiently transmit through. Due to
introduction of incident light, two kinds of incident light are
caused, i.e. near field light caused through the opening of the
shade film 65 and inverted in phase by transmitting through the
phase shifter 63 (referred to as first near field light) and near
field light caused through the microscopic aperture 64 (referred to
as second near field light).
[0078] Particularly, in this case near field light 66 produced
through the microscopic aperture 64 is positioned on the data mark
41 of the recording medium 60 to thereby cause scattering light
(propagation light). The scattering light is detected by a
not-shown photodetector, thus achieving recognition of the data
mark 41.
[0079] Referring FIG. 10, there is illustrated a relationship
between above-mentioned first near field light and second near
field light. The amplitude of near field light (first near field
light and second near field light) in a fully close position to the
microscopic aperture 64 can be expressed rectangular as ideally
shown in a near-field light amplitude distribution (at microscopic
aperture) of FIG. 10. In the near-field light amplitude
distribution (at microscopic aperture), in a plus region is shown
second near-field light while in a minus region is first near field
light. That is, first near field light transmitted through the
phase shifter 63 has an inverted phase by 180 degrees with respect
to second near field light produced through the microscopic
aperture 64.
[0080] With respect to this, a near-field light amplitude
distribution (on medium-surface) of FIG. 10 illustrates an
amplitude distribution of near-field light reaching the recording
medium 40, that is, an amplitude distribution of first near-field
light and second near-field light in a position that a given
distance is provided between the near-field optical probe 40 and
the surface of the recording medium 40. As concerned with second
near-field light is exhibited a spread smoothly attenuating left
and right with a maximum point given on a center axis of the
microscopic aperture 64 in a plus region. For first near-field
light is exhibited a spread smoothly approaching 0 at edges of the
phase shifter 63 and shade film 65 in a minus region.
[0081] Meanwhile, a near-field light intensity distribution (on
medium surface) of FIG. 10 shows a distribution in intensity of
first near-field light and second near-field light offered due to
the above near-field light amplitude distribution (on medium
surface). That is, shown is a sum of near-field light amplitude
produced by transmission through the phase shifter 63 and
near-field light amplitude produced through the microscopic
aperture. 64. As is shown, second near-field light is cut in spread
of near-field light at the edges of the microscopic aperture 64 due
to a presence of first near-field light through the phase shifter
63 in the minus region, thus providing near-field light distributed
with greater sharpness.
[0082] As explained above, according to the near-field optical
probe 60 of Embodiment 5, the opening for causing near-field light
is formed by locally coating the shade film 63. The phase shifter
63 is formed in a manner closing the opening, which is transparent
for a wavelength of incident light to be introduced to the
through-hole 62 to cause shifting by 180 degrees in laser light.
The microscopic aperture 64 is provided through the phase shifter
63. Accordingly, in the case that the reproducing scheme to be
adopted in a near-field light information reproducing apparatus is
taken an illumination mode, cancellation is made between spread in
near field light produced through the microscopic aperture 64 and
spread in near-field light transmitted through the phase shifter
63, at their respective edges. Thus, it is possible to obtain
near-field light with sharpness. This can provide interaction more
locally to the data mark 41 arranged on the recording medium 40. It
is therefore possible to reproduce information from the recording
medium 40 having the data marks 41 recorded with density.
[0083] In the above explanations, the near-field optical probe of
Embodiment 4 or 5, capable of producing near-field light with local
sharpness, can record information with density, for example, to a
recording medium which is coated with a phase change film capable
of producing from a data mark by a comparatively great intensity of
light illumination in addition to reproduction of information on
the rewarding medium.
[0084] As explained above, according to a first recording medium of
the invention, cancellation is made between spread of near-field
light caused on the recording medium due to incident light
transmitted through the phase shifter regions and spread of
near-field light caused on the recording medium due to incident
light transmitted through the transmission regions. This makes it
possible to improve the contrast of near-field light in the areas
that the data marks 21 are adjacently provided. Due to this, an
effect is provided wherein a recording medium can be provided which
is reduced in distance between the adjacent data marks and hence
improved in recording density.
[0085] Also, according to a second recording medium of the
invention, the shade film is coated on a surface of the data mark
arrangement layer in areas except for the data marks and those
where data marks are possible to provide. Accordingly, an effect is
provided wherein a recording medium can be provided that near-field
light only is obtained on a surface of the recording medium for
illumination light incidence under other conditions than total
reflection.
[0086] Also, according to a third recording medium of the
invention, cancellation is made between spread of near-field light
at edges of the data marks as units of the information being
recorded and spreads of near-field light at edges of the phase
shifter. This makes it possible to improve the contrast of
near-field light through the data marks. Due to this, an effect is
provided wherein a recording medium can be provided that the
distance is reduced between the adjacent data marks and hence
improved in recording density.
[0087] Also, according to a first near-field optical probe of the
invention, cancellation is made between spread in near field light
produced through the microscopic aperture and spread in propagation
light transmitted through the phase shifter, at their respective
edges. Thus, it is possible to obtain near-field light with
sharpness. This can provide interaction more locally to the data
mark as information unit arranged on the recording medium. Thus, an
effect is provided wherein a near-field optical probe can be
provided that information can be reproduced from the recording
medium having the data marks recorded with density.
[0088] Also, according to a second near-field optical probe of the
invention, cancellation is made between spread in first near field
light transmitted through the phase shifter and spread in
near-field light produced at the second microscopic aperture, at
their respective edges. Thus, it is possible to obtain near-field
light with sharpness. This can provide interaction more locally to
the data mark as information unit arranged on the recording medium.
Thus, an effect is provided wherein a near-field optical probe can
be provided that information can be reproduced from the recording
medium having the data marks recorded with density.
* * * * *